The Prototype FishPi will be the first ocean-going model. Whereas the The Proof-Of-Concept Vehicle (POCV) is destined for lakes the Prototype will go to sea. The Prototype will also feature a solar panel in addition to batteries.
Features, Functions, & Concepts.
The Prototype is expected to run on a core system of;
- Raspberry Pi - The Raspi will handle all command & control functions. Including navigation, power management, device control, & data logging.
- Batteries - Electronics, including the propulsion system will run from battery. We expect to use a Lithium-ion polymer cell pack.
- Solar Power - The batteries will be charged from an onboard solar panel.
- Drive System - Propulsion is expected to feature a ducted Kort propeller as their design is well suited to low speed and high thrust applications.
- Communications & Telemetry - Ship-To-Shore communication via satellite. One of the project's aims is to be able to transmit images back from the FishPi.
The Raspberry Pi is a single-board computer developed in the UK by the Raspberry Pi Foundation with the intention of stimulating the teaching of basic computer science in schools. The Raspberry Pi has a Broadcom BCM2835 system on a chip (SoC), which includes an ARM1176JZF-S 700 MHz processor, VideoCore IV GPU, and 256 megabytes of RAM. It does not include a built-in hard disk or solid-state drive, but uses an SD card for booting and long-term storage. Wikipedia
Lithium-ion polymer batteries, polymer lithium ion, or more commonly lithium polymer batteries (abbreviated Li-poly, Li-Pol, LiPo, LIP, PLI or LiP) are rechargeable (secondary cell) batteries. LiPo batteries are usually composed of several identical secondary cells in parallel to increase the discharge current capability, and are often available in series "packs" to increase the total available voltage. This type has technologically evolved from lithium-ion batteries. The primary difference is that the lithium-salt electrolyte is not held in an organic solvent but in a solid polymer composite such as polyethylene oxide or polyacrylonitrile. The advantages of Li-ion polymer over the lithium-ion design include potentially lower cost of manufacture, adaptability to a wide variety of packaging shapes, reliability, and ruggedness. Wikipedia
Solar power is the conversion of sunlight into electricity, either directly using photovoltaics (PV), or indirectly using concentrated solar power (CSP). Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Photovoltaics convert light into electric current using the photoelectric effect. Commercial concentrated solar power plants were first developed in the 1980s. The 354 MW SEGS CSP installation is the largest solar power plant in the world, located in the Mojave Desert of California. Other large CSP plants include the Solnova Solar Power Station (150 MW) and the Andasol solar power station (150 MW), both in Spain. The 214 MW Charanka Solar Park in India, is the world’s largest photovoltaic plant. Wikipedia
A ducted propeller, also known as a Kort nozzle, is a propeller fitted with a non-rotating nozzle. It is used to improve the efficiency of the propeller and are especially used on heavily loaded propellers or propellers with limited diameter. It was developed by Luigi Stipa (1931) and Ludwig Kort (1934). The Kort nozzle is a shrouded, propeller assembly for marine propulsion. The hydrodynamic design of the shroud, which is shaped like a foil, offers advantages for certain conditions over bare propellers. Advantages are increased efficiency, better course stability and less vulnerability to debris. Downsides are reduced efficiency and course stability when sailing astern and increase of cavitation. Ducted propellers are also used to replace rudders. Wikipedia
A communications satellite (or COMSAT) is an artificial satellite stationed in space for the purpose of telecommunications. Modern communications satellites use a variety of orbits including geostationary orbits, Molniya orbits, other elliptical orbits and low (polar and non-polar) Earth orbits. For fixed (point-to-point) services, communications satellites provide a microwave radio relay technology complementary to that of communication cables. They are also used for mobile applications such as communications to ships, vehicles, planes and hand-held terminals, and for TV and radio broadcasting, for which application of other technologies, such as cable television, is impractical or impossible. Wikipedia
In The Beginning
What do we want The Prototype to do, and how do we want it to do it?
- Autonomous Navigation.
The FishPi must be able to operate at sea completley independantly. The Raspberry Pi will use multiple devices to navigate the seas.
- Solar Power.
FishPi will use a solar panel to charge batteries onboard. These will then be used to power the vessels drive systems, and any command & control modules.
- Monitor The Surroundings.
There are a considerable amount of possibilities when it comes to environmental monitoring. Some of the options include; air & sea temperature, light monitoring, sea salinity, Ph levels, hydrophones, imagery, barometric monitoring, and many more. Some of the data could be relayed real-time using telemetry.
- Satellite Telemetry.
The use of an independant basic telemetry system would be a huge advantage if a complete system failure occures. Having an independant system which can report basic positioning information, and if possible enviromental information back to the controller without input from the Command & Control systems inside the FishPi. In the event that the battery power is exhausted tracking will still function. Two-way communication opens up real-time course correction, disater avoidance, and most importantly the ability to turn functions on & off, and perform preprogrammed tasks on command.
- Images Over The Amateur Radio Satellite Network.
Transmitting recent images captured aboard the FishPi using the Amsat network. A system like this would be able to broadcast images to anyone who has an antenna, a receiver, and a computer able to decode the signals. A receiver station can be acheived with relativley little expense, in fact at UK Amsat there is a USB receiver capable of receiving transmissions, maybe even on a Raspberry Pi (link).
- Command & Control - Raspberry Pi
- Real-Time Telemetry - yellowbrick | Spot Messenger
- Image Proliferation - Amateur Radio Satellite
- The Hull - Autoclaved Carbon Fibre
- Solar Panel - Enecom HF 130
There is currently no set design for the prototype sea-going FishPi hull. Discussions about the hull on the forums are here.
These designs have been suggested by users on the FishPi forum.
Solar power to The Prototype FishPi will come from a single 130 watt panel producing just under 17 volts, details can be found at Enecom.
The Proof-Of-Concept Vehicle's proplusion system is as below;
- Motor: MFA 919D 540 Motor With Attached Single Ratio Metal Gearbox 2.5:1.
- Propulsion: Raboesch Brass 4 Bladed Kort Propeller RH A-Type Blades (40mm Diameter M4 Thread).
- Propshaft: Raboesch Waterproof Propshaft (186mm M4 Thread).
The Prototype's is as yet unconfirmed. However several possibilities are being considered including the use of ROV thrusters. The threat of blockages, and or damage to the blades of any propellers used by The Prototype means that the use of a ducted system is more than likley.
Commercially available thrusters
There are several systems being considered for use in the sea-going FishPis;
Navigation requires the following component information:
To generate a course:
To ensure you are keeping to that course:
Mapping can be locally stored with waypoints and hazards. This should be in a concise format to enable low bandwidth updating, as this information is critical it should be compared with a hash to ensure there is no data corruption during the transfer.
Primary position fix should be though GPS, there are a number of USB, RS232 or UART devices available. Secondary position fix can be through a calculation of day length. Midpoint of the day can be compared with an offset from GMT to give longitude and day length and date can be used to calculate latitude with varying accuracy.
Solar navigation relies on an accurate clock and a method if recording the position of the sun at sunrise and sunset as this can be used to calculate the day length and zenith.
The solar zenith is local midday or 12pm local time. If you have an accurate clock set to GMT you can calculate the difference and then the longitude as each hour difference equals 15 degrees east or west of 0 (the Greenwich Meridian). Example python to calculate longitude is below:
def calculate(hours,minutes,seconds): if (hours >=24): return "Error" elif (hours >=12): hours=hours-12 minutes = minutes + (hours*60) seconds = seconds + (minutes*60) longitude = (seconds/float(60))/4 elif (hours < 12): hours = 11 - hours minutes = (59-minutes) + (hours*60) seconds = (60-seconds) + (minutes*60) longitude = 0-(seconds/float(60))/4 return longitude
Latitude must be calculated using an iterative process where location is guessed and then day length is calculated, a closer guess can then be made and the process repeated.
Direction cal be found with a simple electronic compass IC such as HMC6352 and compared with actual course information from logged position coordinates.
Batteries in the The Proof-Of-Concept Vehicle (POCV) are 5000mah NiMh SubC cells. Six will be used to generate 7.2 volts.
The Prototype is expected to use Lithium-ion Polymer cells to reduce any possible harm if the FishPi sinks. The exact power rating for The Prototype has not been decided.